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Home > FAQ / Knowledge > A guide to polishing HIF needles --Edited July 2008--

Turbo Tel

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I have been doing this for weeks and seem to have cracked it..

There is a good book on this, "how to build and power tune SU carberettors" by Des Hammill it covers the subject wonderfully but not the extra problems with a turbo setup.



Select a starting needle that is basically lean, Burlen have them at reasonable prices. get a few!! A BDD would be a good start for most but if you choose to plug the part throttle lean pipe you may need something leaner. Either way will work but I found plugging it does most of the work for you and it eliminates a leanout at part throttle that I had trouble with with it still connected.
Also at this point select a spring, I feel that the standard 8oz is fine up to 12psi or so, maybe a 12oz would be needed for some engines esp with higher boost. the point here is to get a spring that allows the piston to reach the fully open position, a spring that is too strong may indeed enrichen the mixture but it does this by choking the engine.. much better to adjust the mixture with the needle.

To make the indicator stick print this image up, make it the same size as a real needle (on my printer image height set to 2.55")



Measure your needle using the 16 "stations" as a guide Just hold the micrometer over the paper with the front edge of the anvil lined up with a station, and close it down, until the needle when pushed in lines up with the image. Thats your reading at that station. In this case 2.25mm at station 4



In the end I made up a measuring pad of hard foam sheeting that made the measurements more repeateable as it held the needle in a fixed position with the end slightly raised.



At this point you need to be able to see how high the piston is sitting. The following procedure will cover stations 1-4 and most of your cruising ponts but after that a turbo starts blowing and it will not work. To see the piston lift at all points of drive this I made a sealed indicator see this post.

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=231607


Next using another of the images make a stick with the same measuring points on it.



before you re-install the dashpot, take a look at how far down the jet is from the bridge (hopefully you have previously installed the needle and established the idle setting) install the needle and dashpot, insert the stick and adjust it to leave about the same amount showing above the dashpot like this..



Now start the engine and warm it up, you will see that the stick moves up and down according to the lift of the piston, the lines give you a good idea which "station" is currently in use, here we are at about station 6. Dont forget that without the damper the engine will stutter if you snap the throttle so move it slowly.

Edited by Turbo Tel on 14th Jul, 2008.

website:- http://www.terryhunt.co.uk


Turbo Tel

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Now you can start checking. slowly raise the rpm and hold and note what happens at 1500, 2000, 2500 etc up to 4000, also note what station is showing. If you have a wideband great its easy just look for 14.7 if you have a narrow band still Ok just see if its lean or rich. If you have neither then you can still detect a lean condition by the engine note, it will hesitate-stutter but good luck with that!! If its lean, great you can polish, if its rich then you probably want to get a leaner needle to start with.

Once you have an idea of what stations need polishing down you can start. Take the needle, lightly mount it in a drillpress (I held onto the needle as I started the drill, and used my fingers to centre it) and use the paper to give yourself an idea where to polish use some 600 grit wet-n-dry (note-- here I am on a much higher station than you would normally be for this part of the proceedings)




Give it a squeeze for around 5 seconds, I found this gave about a 0.01mm correction.



I found 5 secs to be enough for a small adjustment, its much more sensitive at the lower stations than higher, but you have to experiment here. Dont try to do it all at once, keep re-installing and testing it. Make sure you dont over do one area, it must taper down the whole needle. Because of the mechanics of the carb you are probably only going to be using stations 1-12 or 13. I also started marking any stations I did not want to touch with a sharpie pen, eg if I wanted to only polish stations 6-12 I marked 5 and as long as I did not polish off the mark all was well.

When you try this over 4000 you will probably notice that the turbo starts blowing and the piston shoots up. Not much you can do here except install the damper piston to check 5000 and 6000, hopefully by them you will have an idea what station to work on next. I found that 1,2 is idle 3-5 is cruise and it almost equates to the 1000 rpm (i.e. 4000rpm was station 3 1/2 , 6000 was station 5) Try to leave 1-2 alone as it will skew the whole profile (unlesss thats what you want!) keep repeating till you can set any rpm and the mixture is correct at 14.7. With a narrowband keep adjusting each station till you see it change from lean to rich, time to stop! This should get your midrange cruise at around (exactly?) the right points.

Once you get this done road test (dont forget the dashpot oil and look at the other comments in this post regarding oil thickness affecting the profile) and you will probably find that the car cruises nicely in all gears all rpms, except maybe above 3500 in 4th gear where the engine load is a bit higher. However it will probably lean out when you squeeze the throttle.

Next you need to work on the next station which covers light acceleration, in my case station 6-8. then go for a 3/4 throttle acceleration station 9-10, and finally full throttle which should be around station 12 unless you have the wrong spring fitted.
Double check the midrange/cruise as you adjust to make sure you are not affecting them.

Edited by Turbo Tel on 13th Jul, 2008.

website:- http://www.terryhunt.co.uk


Turbo Tel

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If you have built the piston lift indicator http://www.turbominis.co.uk/forums/index.php?p=vt&tid=231607 then you can now really dial in the needle.

For this stage use a light oil, maybe 5w30 or 10w30 synthetic. This will allow the piston to settle quickly. you can use a thicker oil later-- standard SU oil is 20wt

Drive the car in third gear and accelerate just enough so that the piston sits at one of the stations, start at number 6.and check them one at atime. once you have held it for a few seconds to allow the oil damping effect to stabilise take a quick glance at the O2 reading. I found that a small tie-wrap around the indicator at the number I was interested in helps (as my eyes ar not as good as they used to be!!) this will tell you what to do at each station. Try to set an AFR reading a little leaner than what you want to see in the final profile I went for an AFR of 13 as I was looking for 12.5 once I was done, Plus its easyer to enrichen it later rather than lean it.

*indifferent*Note that I set the cruise stations 2-5 at 14 or so and the accelleration stations 6-13 at 13. this seemed to work better for me.

On my engine I found that 0.03mm gave me a change of around 1 on the AFR meter, but all engines are not the same...

Now do this again for every station 6-12, Once they are all done and you have found the right oil for your ebgine you will probably have a nice mixture all the way on a full blown race off the lights.

You should be looking for an AFR of around 12-12.5 for power. under 12 is safe but its not as efficient. over 13 is not desireable as it can cause raal bad detonation problems.


Now take some time to assess the situation, you may have a few leanouts when you floor the accellerator, first try some thicker oil but much thicker than 20wt is probably not wise as it affects the response of the engine. If the car still leaning then find out what station its at when it leans and enrichen it a little. I found that stations 5 and 6 had the biggest influence on these situations but check yours, all engine builds are different. In the end this may cause some rich high speed cruise AFR's but if needs must..

Attached is an XL file of my final needles, you can use this to track your own..


In the end I ruined around 8 needles to get it right! hopefully this guide will help you do it quicker..

Comments welcome..


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Edited by Turbo Tel on 14th Jul, 2008.

website:- http://www.terryhunt.co.uk


Bat

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Hi,
Excellent guide!
Cheers,
Gavin :)

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Brett

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woohooo lol i understand :)
what book are you using haynes for su carbs?
sounds like an interesting read*tongue*

Yes i moved to the darkside *happy*

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matty

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This should come in very handy...in the very near future..good work. *wink*

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stevieturbo

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Will the dashpot be in the same position with a load on the engine though ??


I always just guessed and filed the back of my needles *happy*

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Turbo Tel

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On 8th of Jun, 2007 at 02:26pm stevieturbo said:
Will the dashpot be in the same position with a load on the engine though ??


That procedure gets the low/cruise in and yes it seems to work as any load at say 3000 rpm makes it go the the 4000 spot and thats also correct. but when you start really loading the engine the piston lifts even higher and you are working on the pointy end so you need to also polish stations 8-12 to suit the engine high loaded positions.

The book I used is at the top of the post. Des Hammill, how to powertune SU carbs" or something

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Brett

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On 8th of Jun, 2007 at 04:58pm Turbo Tel said:

The book I used is at the top of the post. Des Hammill, how to powertune SU carbs" or something

lol maybe i should learn to read instead of skipping to the pictures :)

Yes i moved to the darkside *happy*

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Turbo Tel

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Every time I do this I learn more.....

I am finding that stations 1-4 cover idle to cruise at 4000rpm.

Stations 6-8 cover the point where you are cruising and you squeeze the throttle.

Station 10 covers light accelleration with boost

Station 12 WOT


There seems to be a large step between station 8 and 9 where the turbo comes in and thats proving to be a difficult transition. I seem to be having success by sneaking up on it from the higher numbers, i.e moving that shoulder slowly up towards 8.
<<EDIT>> I ended up moving the shoulder all the way to station 6 to eliminate the hesitation, the boost was not a factor.


terry

Edited by Turbo Tel on 22nd May, 2008.

website:- http://www.terryhunt.co.uk


Turbo Tel

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UPDATE..

Well this polishing business is not easy!!

I am finding the cruise and full boost points easy to find but the transition between offboost and boost is a pig to get right. I am finding that the transition area (where the needle gets significantly thinner) has moved up the needle quite a bit from the standard BDD, My theory is that the reason is the GT15 is spinning up relatively quicker, but its a shit to get it spot on. Every time I blow one I learn some more but I'm on my last needle now, a new BDDa nd I'm taking it slowly. Its a little lean on full boost and there is still a ghost of hesitation at the transition but its good so far.

Once I get it where I want I'll post the sizes.

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TurboDave16V
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Tel - I struggled like hell when i switched back from EFI to a carb - I ended up what is almost a step between the 'off boost' and 'on-boost' transition. I never had that problem on the T3

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stevieturbo

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The fuel robbing thing is obviously an issue.

But what about using injectors, to supplement/fine tune the SU's performance ? ( or a single injector at the mouth of the carb ?

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Turbo Tel

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On 9th May, 2008 TurboDave said:
Tel - I struggled like hell when i switched back from EFI to a carb - I ended up what is almost a step between the 'off boost' and 'on-boost' transition. I never had that problem on the T3


Was that with the T2 Dave?

Another observation is that it wasn't nearly as bad without the intercooler. It was there, but the intercooler definitely exaggerated the transition. I almost have it licked but one false move here and I have blown another needle!! I'm going to take it real easy from here..

Edited by Turbo Tel on 9th May, 2008.

website:- http://www.terryhunt.co.uk


Turbo Tel

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On 9th May, 2008 stevieturbo said:
The fuel robbing thing is obviously an issue.

But what about using injectors, to supplement/fine tune the SU's performance ? ( or a single injector at the mouth of the carb ?


Fuel robbing?? I know what that is but how does that pertain? tell me more!!

website:- http://www.terryhunt.co.uk


robert

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tel ,
what im running at the mo is , a filed bdd ,around a 2mm flat down from idle to 3/4 then a tapering falt to the tip ,

to get the cruise ok i ran the mid range lean off tube to the side port and then a t piece on this to a valve in the car to adjust vacuum on the float bowl at cruise , the valve is wide open and its just about ok.. a touch on the edge of lean misfire ,with a jolt on it supplying sparks .

i also used a thick vr1 20/50 in the dashpot ,and stuck on another brass spacer on the piston of the damper rod ,so the piston had half normal free play . this whole setup feels pretty good all round and gives me 40 mpg .hope that helps
regards robert

oops forgot to say , im running the avonbar 15 psi spring ,which i think is the green one , i look at the spring weight needed in terms of airflow cfm needed ,not boost level , so if a nat asp mini puts out 100 bhp ,then the spring for that would do for a turbo mini that would make 100 nat asp ... if that makes sense !

Edited by robert on 9th May, 2008.

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Paul S

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On 9th May, 2008 Turbo Tel said:
I am finding the cruise and full boost points easy to find but the transition between offboost and boost is a pig to get right. I am finding that the transition area (where the needle gets significantly thinner) has moved up the needle quite a bit from the standard BDD, My theory is that the reason is the GT15 is spinning up relatively quicker, but its a shit to get it spot on. Every time I blow one I learn some more but I'm on my last needle now, a new BDDa nd I'm taking it slowly. Its a little lean on full boost and there is still a ghost of hesitation at the transition but its good so far.


I think that the problem is that you go from NA mode where the piston is lifted by the venturi effect velocity over the bridge to a pure pressure balance mode under boost with the piston lift determined by the restrictor ring.

Both modes are probably using the same part of the needle, but want different fuel delivery.

Just thinking out loud really, but you could try adjusting the restrictor ring bore diameter. If you make one up slighly smaller bore it may pull the piston higher under boost.

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Turbo Tel

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On 9th May, 2008 Paul S said:


Just thinking out loud really, but you could try adjusting the restrictor ring bore diameter. If you make one up slighly smaller bore it may pull the piston higher under boost.


Hmm.. that would seperate the area of the needle used in N/a mode from boost mode.. or would it cause a bigger transition problem because the piston raises faster as the boost comes in??
I need to take a closer look at the boost guage as it happens..

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Turbo Tel

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I have been able to look at this clearer now with my piston lift indicator http://www.turbominis.co.uk/forums/index.php?p=vt&tid=196857 and I am finding that the problem "transition" is not just due to boost, it seems that the engine just needs a lot of fuel here and the dashpot oil cant provide it alone. I now know that stations 1-5 are the cruise spots and when you floor it from cruise stations 6-7 are the first ones to come in. I polished them up some more and things are improved, though I suspect that real high speed cruise may be getting rich, I need to get on a motorway to check that.

I am also surprised at how much thicker dashpot oil affects the WOT needle profile. The piston is always lagging a bit because of the oil and I am finding that in normal driving with 20/50 oil the piston never really catches up, except perhaps when you hold it WOT in top gear for a while where I am seeing a leanoff when the piston finally catches up.. (in 1st 2nd 3rd you cant hold it long enough to see this) Therefore I am now trying to set this up with 10/30 oil to minimise that effect. maybe go even thinner if I can..

I remember seeing posts asking about leanoff in top gear, I bet thick oil is the reason..

Next, I plan to play with a 12oz spring, see what that does..

Edited by Turbo Tel on 20th May, 2008.

website:- http://www.terryhunt.co.uk


clubman_dan

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nice guide, regarding dashpot oil, i was advised at a rolling road recently that hydraulic jack oil is the stuff to go for, may be worth a try?


Turbo Tel

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On 20th May, 2008 clubman_dan said:
nice guide, regarding dashpot oil, i was advised at a rolling road recently that hydraulic jack oil is the stuff to go for, may be worth a try?


Why not.. Its just down to how viscus it is, Auto transmission oil has been mentioned as well, also a mix of Autotx/20-50 to get the required viscosity. I'll play with that as well, I'm thinking the lighter the oil the better

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Sir Yun

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but lighter oil wil make the piston rise quicker thus not enriching the mix more at acceleration..

anyways the oil and needle seem to have to matched. something full synth would make sense to keep the viscosity constant over a wide range.

hmm magneto rheologic SU carb damper..*tongue* now that would be needlessly expensive

Edited by Sir Yun on 20th May, 2008.

That sir, is not rust, it is the progressive mass reduction system

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Turbo Tel

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On 20th May, 2008 Sir Yun said:
but lighter oil wil make the piston rise quicker thus not enriching the mix more at acceleration..



Yup!!!

Oil thats too thin will cause hesitation. The question is -- whats too thin!! Is the hesitation due to oil or a bad profile?

As I am polishing the needle I can adjust it to suit, but from what I am seeing, the oil viscosity and needle need to be matched.

Terry

website:- http://www.terryhunt.co.uk


Turbo Tel

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OMG this is REALLY REALLY REALLY Hard!!!

OK so now I have a good visual on the piston position the experiments have started. Remember this is 9psi with a GT15 turbo. 8.5 CR 2.95 diff.

First the spring. I tried a 4oz, 8 oz, 12oz. Bottom line is they will all work--If you profile the needle to suit. Taken to its extreme the racers use 2 oz springs with no oil (or 3-in1 oil). this is because they want instant throttle response, however there are compromises such as crap low rpm response. rich a heck cruise, but they dont care, they are full throttle all the time.
I found all 3 got fully open the 4oz was a bit early, the 12 oz didnt make it in top gear and it relly felt sluggish to me so I plumped for the 8oz.

Next the oil, This has a HUGE effect on your profile. I started with 30wt and had bad leanoff in top gear, I went to 10/30 and had to shave the needle bigtime but was able to get a nice running profile. cruise was great, WOT was great but I could not cure a horrible leanout if I held the throttle to just give half boost on the gauge. SU oil is 20wt so I tried 20/50 and Bingo.. the leanout has gone.. But because of the thicker oil I am a bit rich (AFR 11) at WOT with that needle. The difference from 10, 20, 30 wt oil is big. I would say its AFR 14-12-10 with a given needle. So my advice is stick with 20wt oil when polishing, you can adjust it later to suit, (maybe a bit thicker in summer, thinner winter?)

Now the actual profile, I have been fighting the leanoff when you floor it from cruise and found that in my case (remember this is a GT15 and its probably spinning up a bit quicker) I need extra fuel at stations 5-8. Problem is station 5 is in the 70mph cruise area so there seems to be a compromise here, plus you are rapidly dropping down to not far above that requred for WOT and you need to maintain them a bit leaner to allow for a nice progression down to station 12 which is WOT.

Heres an Idea where I am. This graph shows a BDD, my current needle BDD#2, an Avonbar10psi (which bytheway was unusable rich at idle till I adjusted stations 1,2)and my previous needle, which I intend to work on some more. I'll probably follow BDD#2 until station 8 but keep a bit leaner from there on measurements are in mm (cos I only have a metric micrometer!!)



Attached is an Xcell file..


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Edited by Turbo Tel on 22nd May, 2008.

website:- http://www.terryhunt.co.uk


robert

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really fascinating tel ,thanks for sharing this .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Home > FAQ / Knowledge > A guide to polishing HIF needles --Edited July 2008--
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